1. Field of the Invention
The present invention particularly relates to a single chip microprocessor comprising a central processing unit and a means for implementing its peripheral functions embedded in the same semiconductor package as the central processing unit and relates to a method for setting up the peripheral functions of the microprocessor. The invention thus relates to an effective technology applicable to a technique for coping up with the user's typical need for facilities for setting up and modifying operational specifications and functions of the microprocessor.
2. Description of the Prior Art
In the case of a microprocessor such as a single chip microcomputer comprising a CPU (Central Processing Unit) as a core and necessary peripheral circuits embedded in a single semiconductor package, electrically writable read-only memory known as EPROM is used as program memory for storing its software programs so as to allow the programs to be modified and program bugs to be corrected. A technology allowing external code to be written into such EPROM has been disclosed in Japanese Patent Laid-open No. 60-198667.
By the way, in recent years, while the microcomputer application system is becoming versatile and even smaller in size, there is every indication that the number of applications of single chip microcomputers embedding a variety of on-chip hardware peripheral circuits is increasing more and more. As a result, the single chip microcomputer has got to embed a variety of hardware peripheral circuits configurable also as logic external to the CPU such as interface circuits, timers, counters, and serial input/output control circuits. However, even though software stored in EPROM program memory can be modified, the hardware peripheral circuits embedded in such a microcomputer, particularly functional portions of the hardware logic, are fixed. Therefore, the overall design of the microcomputer and a master pattern for manufacturing use must inevitably be modified in order to change logical functions of the embedded hardware. As a result, the microcomputer user can neither by himself set required operational specifications and functions into the functional portions of the embedded hardware logic nor even modify them. In addition, there is a lack of flexibility in coping with needs to modify operational specifications and functions of a microcomputer application system during the development phase of the system. Being aware of such problems, the inventors of the invention studied a technique for implementing required peripheral functions through software which is stored into electrically writable non-volatile memory elements in their writable state. Viewing the problems one step further from the standpoint of implementing peripheral functions that should essentially be defined by the user, the inventors of the invention identified a need for a technology that allows the peripheral functions to be defined more easily or a technology that allows the peripheral functions to be used in the user's own way. In addition, the inventors of the invention also recognized a need to implement the peripheral functions by means of software in a general sense, consuming only low power as well.